a) Field of the Invention
The invention relates to a digital audio/video playback system and, more particularly, to a digital audio/video playback system capable of controlling audio and video playback speed.
b) Description of the Related Art
Advancement in information technology has enabled sounds and images to be stored, transmitted, and played back in digital format. Besides providing higher definition films, digital audio/video format further provides many additional functions. Taking digital versatile disc (DVD) as an example, it not only stores high definition films but also collects multilingual soundtracks and multiple sub-pictures for users to select for playback. One of the main functions of the sub-picture is to be used as subtitle. For example, since English and Chinese soundtracks as well as English and Chinese subtitles are collected in an English language family film, an user can select to playback the film in English with Chinese subtitle, in English with English subtitle, or in Chinese with either English or Chinese subtitle. Thus, the film can be internationalized more easily.
Referring to FIG. 1, a conventional digital audio/video playback system 1 includes a loader 11, a parser 12, a video decoder 13, and an audio decoder 14. The loader 11 is used to receive a digital audio/video signal (DAVS). The parser 12 is used to resolve the DAVS into a video bitstream (VB) and an audio bitstream (AB). The video decoder 13 receives the VBS and decodes it to a decoded video (DV), whereas the audio decoder 14 receives the ABS and decodes it to a decoded audio (DA). The DV and DA are then output to an output device 2.
The aforementioned DVD with multiple soundtracks and subtitle tracks collected therein can be played back with its sound and subtitle in different languages, and therefore the DVD can serve a language learning purpose according to the user's need. For example, when a movie is played back in English with English subtitle, the image, sound and subtitle information can be simultaneously received at the user's end to enhance the learning effect. However, the conventional DVD playback system only plays back video (including picture and subtitle) and audio simultaneously at a normal playback speed. If a movie is played back at a slower playback speed, mostly only video is in slow motion but no audio is output, resulting in a silence status or a seriously distorted output audio like lowered tone, mumbled or intermittent sound. Thus, the effect of language learning is greatly affected since the user is unable to simultaneously receive accurate and clear video and audio. On the other hand, if the movie is played back at a higher playback speed, also only video is output but not audio, or the output audio is distorted, for example, too high and sharp tone that is difficult to be recognized.
Summing up the above, there is a need to create a digital audio/video playback system capable of adjusting the audio/video playback speed while outputting video and audio with minimized distortion of output audio.